New research by Ryan Schacht is reported in the New Scientist

More men inevitably means more testosterone-fuelled violence, right? Wrong, according
to a comprehensive analysis exploring how a surplus of men or women affect crime rates
across the US.

In areas where men outnumber women, there were lower rates of murders and assaults
as well as fewer sex-related crimes, such as rapes, sex offences and prostitution.
Conversely, higher rates of these crimes occurred in areas where there were more women
than men.

Ryan Schacht of the University of Utah in Salt Lake City and his colleagues analysed
sex ratio data from all 3082 US counties, provided by the US Census Bureau in 2010.
They compared this with crime data for the same year, issued by the US Federal Bureau
of Investigation. They only included information about women and men of reproductive
age.

For all five types of offence analysed, rising proportions of men in a county correlated
with fewer crimes– even when accounting for other potential contributing factors such
as poverty. The results suggest that current policies aimed at defusing violence and
crime by reducing the amount of men in male-dominated areas may backfire.